1. Field of the Invention
The present invention relates to a substrate and, more particularly, to a substrate for increasing the light-extraction efficiency of a semiconductor light-emitting device.
2. Description of the Prior Art
The current semiconductor light-emitting devices, such as light-emitting diodes, have been used for a wide variety of applications, e.g. illumination, remote control. To ensure high functional reliability as great as possible and a low power requirement of the semiconductor light-emitting devices, the external quantum efficiency is required for the devices.
In principle, the external quantum efficiency of a semiconductor light-emitting device is determined both by the internal quantum efficiency and extraction efficiency. The internal quantum efficiency is determined by the material property and quality. The extraction efficiency refers to the proportion of radiation emitted from the interior of the device into surrounding air or encapsulating epoxy. The extraction efficiency is determined by the losses occurred when radiation leaves the interior of the device. If a total reflection occurred when light is to be emitted out from the semiconductor light-emitting device, light would be reflected repeatedly until being absorbed in the interior of the device, which decreases the external quantum efficiency of the semiconductor light-emitting device.
In the prior art, a surface of a substrate of a semiconductor light-emitting device could be designed to exhibit a particular surface morphology for scattering light emitted out from the semiconductor light-emitting device to reduce the probability of the total reflection, further enhancing the external quantum efficiency of the semiconductor light-emitting device. However, the surface morphology of the above-mentioned substrate is generally formed by a dry etching process or a wet etching process. These processes not only consume much time but cost much.
Therefore, the main scope of the invention is to provide a substrate for epitaxy of a semiconductor light-emitting device, and the substrate is capable of enhancing the light-extraction efficiency of the semiconductor light-emitting device.